The present invention relates to a method and an apparatus for machining a join surface of a workpiece having the join surface.
In joining two members, there is a case where it is necessary to closely attach the surfaces of members made of metal, or the like, to each other or with a rubber seal or a gasket interposed between the two members. In such a case, the join surfaces are generally finished by grinding using a surface grinding machine or a rotary grinding machine.
The use of a grinding tool such as a grinding stone, however, forms fine streaks, on the order of micrometer, called cutter marks or grinding surface marks on the join surface along the direction in which the abrasive grains move.
A vacuum container, called a xe2x80x9cchamberxe2x80x9d and used in a system for fabricating semiconductors or liquid crystal devices, requires a high hermetic property of the join surfaces between the lid and the body of the container. The join surfaces requiring such a high hermetic property are generally sealed with such a seal element as a rubber seal or gasket to prevent leakage.
It has been found that join surfaces finished by grinding in the prior art develops leakage due to the fine streaks described above even in the case where a seal element is used. The streaks caused by the abrasive grains are usually of a size on the order of micrometer and therefore are difficult to completely fill up with the seal. In the presence of a streak providing communication with the interior and the exterior of the container, therefore, a leak is caused.
Specifically, the streaks formed by abrasive grains, if some of them extend in such a direction as to establish communication between the interior and the exterior of the container, are so fine that they cannot be completely filled up with a seal element or the like, resulting in leakage along the streaks.
Accordingly, it is an object of the present invention to provide a method and an apparatus for machining a join surface, by which the leakage attributable to the streaks formed by the abrasive grains is eliminated to provide a highly hermetic join surface.
In view of the object described above, the present invention is characterized in that the grinding process is performed using a grinding tool such that the direction of the fine streaks formed by the abrasive grains substantially coincides with the direction along the outline shape or the outer periphery shape of the area defining the join surface.
Specifically, according to a first aspect of the present invention, there is provided a method, for machining a join surface of a workpiece, which includes the steps of: providing a grinding tool having a rotation axis substantially parallel to the join surface and adapted to rotate about the rotation axis; applying the grinding tool to the join surface of the workpiece to be machined; and grinding the join surface of the workpiece so as to form grinding streaks on the join surface in the direction substantially along the outline shape of the join surface area.
According to a second aspect of the present invention, there is provided a method, for machining a join surface of a workpiece, which includes the steps of: providing a grinding tool having a rotation axis substantially parallel to the join surface and adapted to rotate about the rotation axis; applying the grinding tool to the join surface of the workpiece to be machined; and grinding the join surface of the workpiece by providing the relative feeding movement in a direction substantially along the outline shape of the join surface area between the grinding tool and the workpiece while controlling the direction of the grinding tool or the workpiece such that the direction of the rotation axis of the grinding tool is substantially orthogonal to the direction of the relative feeding movement.
According to a third aspect of the present invention, there is provided an apparatus, for machining a join surface of a workpiece, which includes a spindle having a machining tool removably mounted thereon; a table having the workpiece mounted thereon; a linear feeding mechanism for moving the spindle and the table relatively to each other along the three orthogonal X-, Y- and Z-axes; a rotation mechanism for moving the spindle or the table in the direction along the C-axis as a rotative movement about the Z-axis; a grinding tool having a rotation axis substantially parallel to the join surface and mounted as a machining tool on the spindle to rotate around the rotation axis; and a numerical control unit for controlling the linear feeding mechanism and the rotation mechanism such that the grinding tool forms grinding streaks on the join surface in the direction substantially along the outline shape of the join surface area.
According to a fourth aspect of the present invention, there is provided an apparatus for machining a join surface of a workpiece, which includes a spindle having a machining tool removably mounted thereon; a table having the workpiece mounted thereon; a linear feeding mechanism for moving the spindle and the table relatively to each other along the three orthogonal X-, Y- and Z-axes; a rotation mechanism for moving the spindle or the table along the C-axis as a rotative movement about Z-axis; a grinding tool having a rotation axis substantially parallel to the join surface and mounted as a machining tool on the spindle to rotate about the rotation axis; and a numerical control unit for providing the cut-in movement along the Z-axis and the relative feeding movement along the X- and Y-axes in a direction substantially along the outline shape of the join surface area between the grinding tool and the workpiece while controlling the feeding movement along the C-axis such that the direction of the rotation axis of the grinding tool is substantially orthogonal to the direction of the relative feeding movement.
In the machining apparatus according to the third and fourth aspects described above, the grinding tool is preferably a grinding wheel or a belt grinding tool, and the grinding tool more preferably has a hydraulic motor for rotatably driving the grinding wheel or the grinding belt utilizing pressurized fluid flowing through a central portion of the spindle.
The grinding streaks formed by the grinding tool (or specifically, the abrasive grains thereof), if formed substantially along the outline shape of the join surface area, fail to establish the communication between the interior and the exterior of the container and, therefore, a highly hermetic join surface can be provided.
Further, by providing the relative feeding movement along the outline shape of the join surface area and moving the grinding tool and the join surface of the workpiece relatively to each other such that the direction of the rotation axis of the grinding tool substantially parallel to the join surface is substantially orthogonal to the direction of the relative feeding movement of the grinding tool, the streaks due to the grinding tool (or specifically, the abrasive grains thereof) are always formed along the outline shape, i.e. the outer periphery shape of the join surface area.
When a hydraulic motor is used as a driving unit for rotatably driving the grinding wheel or the grinding belt mounted on the spindle, pressured fluid such as compressed air supplied to the central portion of the spindle can be utilized as a power source. Therefore, the need of independently supplying power from an external source is eliminated, thereby making it unnecessary to conduct a manual mounting operation. As a result, an automatic tool changer can be used.
The term xe2x80x9cgrindingxe2x80x9d herein generally refers to machining using abrasive grains and is defined to include not only machining using a tool such as a grinding stone having abrasive grains but also polishing using a liquid containing abrasive grains. Also, the term xe2x80x9cjoin surfacexe2x80x9d is defined as a joining surface requiring sealability. Further, the term xe2x80x9cgrinding tool in rotationxe2x80x9d is defined to include a tool such as a belt grinding tool with the grinding belt moved along an elliptical or an elongate circular path, and the term xe2x80x9cthe direction along the rotation axisxe2x80x9d of the belt grinding tool is defined as a direction perpendicular to an elliptical or an elongate circular plane formed by the path of the grinding belt or the locus of the abrasive grains.